The present invention relates to a sensor for detecting the direction of rotation of a rotating body, and more particularly relates to a sensor for detecting whether a body is first rotated in the clockwise rotational direction and then subsequently is rotated in the anticlockwise rotational direction, or is first rotated in the anticlockwise rotational direction and then subsequently is rotated in the clockwise rotational direction.
The stimulus for the present invention has come from the development of vehicle turn signal indicators, and in particular from the development of self canceling vehicle turn signal indicators. A conventional direction indicating switch of an automobile or other automotive vehicle is generally mounted on the side of the steering column of the automobile, and usually comprises a control lever which is pushed upwards or downwards by hand by the driver of the vehicle according to the intended direction of turning of the vehicle. Typically, after making a signal which, for example, indicates his or her intention of turning left, and therefore after displacing the aforesaid lever into its anticlockwise biased position, wherein it remains, the driver of the vehicle then turns the steering wheel thereof first in the anticlockwise direction, so as to displace the steering mechanism of the vehicle to turn the vehicle to the left, and then subsequently, when the left turn has been almost completed, turns the steering wheel in the clockwise direction, so as to cancel this positioning of the steering mechanism, in order to straighten out after the left turn. It is conventional to arrange a self canceling mechanism by providing a projection or the like on the steering shaft, which trips the aforesaid direction indicating switch control lever back to its neutral position, during the aforesaid reverse turning of the steering shaft--in this case, the clockwise rotation thereof.
Since such a self canceling mechanism operates by mechanically returning the control lever of the direction indicating switch back to its neutral position when the steering wheel is turned back towards its neutral or straight ahead position, it is necessary for the direction indicating switch control lever to be pivotally mounted to a member proximate to the steering shaft, such as to a steering column outer tube. Accordingly in the prior art the mounting position of the direction indicating switch is extremely restricted, and thereby little freedom in the matter of design for this direction indicating switch has been available.
Nowadays, new conceptual design revolutions have occurred with regard to the instrument panel design of automobiles, in particular; and a strong demand has arisen for a system in which more freedom in arranging the mounting position of the direction indicating switch, or, more precisely, of the base of the control lever thereof, should be available. In other words, rather than the aforesaid prior art mechanical self canceling arrangement, it has become desirable for the flashing of the direction indicators to be electrically maintained, and for this flashing to be automatically canceled after a turn which has been indicated has been completed.
However, one of the difficulties in providing such an electrical direction signaling system is the requirement for provision of a sensor which electrically detects the rotational direction of the steering wheel; in more detail, for a sensor which is able to detect whether the steering wheel has been turned first in the clockwise rotational direction and then subsequently in the anticlockwise rotational direction, i.e. for a right hand turn, or has been turned first in the anticlockwise rotational direction and then in the clockwise rotational direction, i.e. for a left hand turn. Such a sensor should provide an electrical output signal or signals for releasing the electrical retention of the flashing of the direction indicators on one side or the other side of the vehicle.
Further, such a sensor should not be too sensitive. In other words, once a turn has been indicated by the driver of the vehicle via the direction indicating switch by displacing the control lever thereof, then this control lever should not be canceled or returned to its neutral position as a result only of slight motion of the steering wheel; only rotational movement of the steering wheel through an angle larger than a certain angle, in one direction and in the opposite direction, should be effective to trigger the rotational direction sensor to produce its output signal indicating steering rotation of the steering wheel has been finished. If this is not the case, slight to and fro movements of the steering wheel, during or just before a turn, will undesirably cancel the operation of the direction indicators of the vehicle, so that the turn is no longer properly signaled to other vehicle operators.